Imaging device, method of driving imaging device, and method of manufacturing imaging device

Abstract

An imaging device is provided and includes: a photoelectric conversion layer that has a silicon crystal structure and generates signal charges upon incidence of light; a multiplication and accumulation layer that multiplies the signal charges by a phenomenon of avalanche electron multiplication; and a wiring substrate that reads the signal charges from the multiplication and accumulation layer and transmits the read signal charges. The photoelectric conversion layer includes: a first conductive impurity layer containing first impurities in an impurity concentration; an electron acceleration layer containing the first impurities in a lower impurity concentration than the first conductive impurity layer; and a second conductive impurity layer to which a voltage is applied, the second conductive impurity layer containing second impurities and disposed on a side opposite a light incidence side of the electron acceleration layer, and an insulating layer is disposed between the electron acceleration layer and the multiplication and accumulation layer.

1. An imaging device comprising: in order,
 a photoelectric conversion layer that has a silicon crystal structure and generates signal charges upon incidence of light; 
 a multiplication and accumulation layer that multiplies the signal charges by a phenomenon of avalanche electron multiplication; and 
 a wiring substrate that reads the signal charges from the multiplication and accumulation layer and transmits the read signal charges, 
 wherein 
 the photoelectric conversion layer includes: 
 a first conductive impurity layer containing first impurities in an impurity concentration; 
 an electron acceleration layer containing the first impurities in a lower impurity concentration than that of the first conductive impurity layer; and 
 a second conductive impurity layer to which a voltage is applied, the second conductive impurity layer containing second impurities and disposed on a side opposite a light incidence side of the electron acceleration layer, and 
 an insulating layer is disposed between the electron acceleration layer and the multiplication and accumulation layer. 
 
     
     
       2. The imaging device according to  claim 1 , wherein the impurity concentration of the first layer gradually decreases in a direction of incident light. 
     
     
       3. The imaging device according to  claim 1 , wherein the photoelectric conversion layer includes: a low electric field region disposed at a light incidence side of the photoelectric conversion layer; and a high electric field region closer to a side of the multiplication and accumulation layer than the low electric field region, the high electric field region having an electric potential gradient larger than that of the low electric field region. 
     
     
       4. The imaging device according to  claim 1 , wherein the photoelectric conversion layer has a thickness of 5 μm or more. 
     
     
       5. A method of manufacturing an imaging device according to  claim 1 , wherein the photoelectric conversion layer and the multiplication and accumulation layer has a structure in which epitaxial layers, each including a plurality of impurity layers formed by epitaxial growth, are superposed each other, the method comprising:
 sequentially forming impurity layers on a first silicon substrate by epitaxial growth as a first epitaxial layer; 
 forming an oxide layer on a surface of the first epitaxial layer; 
 injecting hydrogen ions between the first silicon substrate and an impurity layer adjacent to the first silicon substrate; 
 bonding the first epitaxial layer via oxide layer to a second epitaxial layer formed on a second silicon substrte; and 
 separating the first epitaxial layer from the first silicon substrate by using a smart cutting method. 
 
     
     
       6. A method of driving an imaging device according to  claim 1 , comprising applying a negative voltage to the first impurity layer in high-sensitivity imaging, wherein an absolute value of the negative voltage is larger than that in normal imaging.